DAO prepress abstract  -  DOI: https://doi.org/10.3354/dao03195

Pathogens of Dikerogammarus haemobaphes regulate host activity and survival, but also threaten native amphipod populations in the UK

Jamie Bojko, Grant D. Stentiford, Paul D. Stebbing, Chris Hassall, Alice Deacon, Benjamin Cargill, Benjamin Pile, Alison M. Dunn*

*Email: a.dunn@leeds.ac.uk

ABSTRACT: Dikerogammarus haemobaphes is a non-native amphipod in UK freshwaters. Studies identify this species as a low-impact invader in the UK, relative to its cousin Dikerogammarus villosus. It has been suggested that regulation by symbionts (such as Microsporidia) could explain this difference of impact. The effect of parasitism upon D. haemobaphes is largely unknown. This was explored herein using two behavioural assays measuring activity and aggregation. Dikerogammarus haemobaphes were screened histologically post-assay, identifying two novel viruses (Dikerogammarus haemobaphes bi-facies-like virus [DhbflV], Dikerogammarus haemobaphes Bacilliform Virus [DhBV]); Cucumispora ornata (Microsporidia); Apicomplexa; and Digenea, which could alter host behaviour. DhBV infection burden increased host activity, and C. ornata infection reduced host activity. Secondly, native invertebrates were collected from the invasion site at Carlton Brook, UK, and tested for the presence of C. ornata. PCR screening identified that Gammarus pulex and other native invertebrates were positive for C. ornata. The host range of this parasite, and its impact upon host survival, was additionally explored using D. haemobaphes, D. villosus, and G. pulex in a laboratory trial. Dikerogammarus haemobaphes and G. pulex became infected by C. ornata, which also lowered survival rate. Dikerogammarus villosus did not become infected. A PCR protocol for DhbflV was also applied to D. haemobaphes after the survival trial, associating this virus with decreased host survival. In conclusion, D. haemobaphes has a complex relationship with parasites in the UK environment. Cucumispora ornata likely regulates populations by decreasing host survival and activity, but despite this benefit, the parasite threatens susceptible native wildlife.